1. Field of the Invention
This invention relates to a novel polyester composition and to sizing compositions utilizing said novel polyester composition on a fibrous article such as a synthetic textile yarn.
2. Description of the Prior Art
Prior to the weaving operation a continuous filament polyester warp yarn is usually given a twist of about 10 to 15 turns per yard and treated with a sizing composition which binds the filaments of the yarn together so as to strengthen the yarn by rendering it more resistant to abrasive forces to which it is exposed during the subsequent weaving operation. It is less expensive to size the warp yarn than to impart a high degree of twist to the yarn in order to reduce the breaking tendency during weaving. Sizing materials, besides conferring abrasion resistance, must have the additional property of being easily removed subsequent to the weaving operation so as to return the yarn to its unsized state in which chemical dyeing treatments are often performed on the woven fabric.
It is common in the textile industry to use as sizing materials easily removed high molecular weight polymers such as polyvinyl alcohol and starch but with the advent of synthetic fibers, especially polyester fibers based upon polyethylene terephthalate, yarns made of these materials are not suitably sized with these conventional sizing materials but require a synthetic sizing material having suitable adhesion to the synthetic fiber as exemplified by those taught in U.S. Pat. No. 3,546,008. Such synthetic sizes have been found difficult to remove by ordinary washing in the presence of caustic soda.
In U.S. Pat. No. 3,546,008 there is disclosed a copolyester containing the residue of a 5-sodio-sulfo-isophthalic acid. This polyester is disclosed as useful as a sizing composition on a textile yarn such as a yarn made from poly(ethylene terephthalate). Such sizing compositions have found acceptance especially for the sizing of textile yarns with which difficulties have been experienced in adhering conventional sizing materials thereto. For instance, the use of the less adhesive starch and polyvinyl alcohol based sizes is found to be relatively ineffective as compared to the polyester size compositions disclosed in said U.S. patent. The size compositions of said patent are those prepared using at least one difunctional dicarboxylic acid sulfomonomer containing a --SO.sub.3 M group attached to an aromatic nucleus wherein M is hydrogen or a metal as disclosed in said patent. These size compositions have exhibited the defect of marginal solubility in the usual caustic solutions such that they are difficult to remove from the fibers.
U.S. Pat. No. 3,779,993 relates to water-dispersible polyesters and polyester amides prepared by reacting a glycol, a dicarboxylic acid, and at least one difunctional comonomer which contains a metallic salt of a sulfonic acid radical which is attached to an aromatic nucleus. However, in column 11, Table 1, it is disclosed that polymer Y can be prepared using a formula illustrated in footnote 11 in which the sulfonate group is attached by an aliphatic chain to a succinic acid ester. Such polyesters can be used as sizing or coating compositions when dispersed in water.
British Pat. No. 1,418,975 is similar to the above in having disclosed therein the preparation of water-soluble sulfonated polyester size compositions comprising (1) polyesters having unsaturated aliphatic bonds which are sulfonated subsequent to polyester formation or (2) polyesters prepared from a sulfonated diester of an unsaturated aliphatic diacid.
The --SO.sub.3 M group where M is a metal has also been incorporated in polyesters suitable for forming fibers according to U.S. Pat. No. 3,018,272 where the group functions as a basic dye sensitizing unit to permit the fibers to be readily dyed using basic dyes. The basic dye sensitizing unit is substituted on either an alkylene radical or an arylene radical. The polyesters disclosed are apparently not water-dispersible.
U.S. Pat. No. 3,147,301 relates to a method of imparting ionic properties to copolymers by reaction of a suitable ethylenically unsaturated vicinal dicarboxylic acid, its anhydride or acyl halide with an hydroxysulfonic acid. Modification of polymers is taught so as to provide slightly ionic or hydrophilic properties in, for instance, an hydrophobic polymer. Such modification also provides improved dyeability and improved antistatic properties in the polymer but there is no disclosure of the preparation of polyesters or water-soluble polyesters.
U.S. Pat. No. 3,033,824 relates to polyester fibers having improved dyeability prepared by the incorporation therein of a mono- or difunctional aromatic compound possessing a sulfonic acid group or its salts, esters or amides. As indicated in column 3, two sulfonate or sulfonamide groups can be attached to the aromatic ring, one directly and one indirectly through a carbonyl group, or a single sulfonate or sulfonamide group can be directly attached to the aromatic ring. Such polyesters are not disclosed as water-soluble.
The polymers of the prior art can be distinguished structurally from those of the present invention and also on the basis that certain polymers of the prior art are hydrophobic and, therefore, would lack the water solubility required for use as a sizing material. The water-dispersible polyester sizes of the prior art contain sulfonate groups attached to the backbone of the polyester by direct substitution on an arylene or an alkylene group of the polymer backbone and, therefore, would differ structurally from those polyesters disclosed herein in which the sulfonate group is attached to an aromatic nucleus through an aliphatic or cycloaliphatic hydrocarbon chain and ester linkage.